1. Field of the Invention
This invention relates to wireless sensors and sensing systems. More specifically, the invention is a wireless tamper detection sensor and sensing system based on an open-circuit defined by an electrically-conductive two-dimensional geometric pattern having no electrical connections.
2. Description of the Related Art
A variety of package tampering detection systems have been developed in recent years. In general, these various systems are designed to allow a manufacturer, shipper and/or vendor/retailer to detect if a package has been tampered with (e.g., package is opened, contents are removed, and package is resealed to conceal the pilferage) in an effort to determine where there may be a problem in the finished-product shipping and warehousing chain. Most of these systems involve some sort of visual marking (e.g., bar code) or electrically-powered sensor that is attached to a package and read/or interrogated. However, the visual mark systems are relatively easy to defeat by careful cutting and restoring of the bar code. Electrically-powered sensor systems tend to be bulky since an electrical power source must be provided.
U.S. Pat. No. 5,541,577 discloses an electromagnetic asset protection system in which a magnetic strip is applied to a package. The magnetic strip can be interrogated by a hand-held scanner that produces an electromagnetic field near the magnetic strip in order to saturate same. The resulting electromagnetic field emanating from the magnetic strip is then read by the scanner. If the magnetic strip is cut, the response read by the scanner will be different than if the magnetic strip is not cut. However, if the entire magnetic strip is removed and then replaced after the package is opened and resealed, there would be no evidence of tampering.